+Example: Declare and initialise a check watcher, utilising the above
+macros so it will work regardless of whether multiple loops are supported
+or not.
+
+ static void
+ check_cb (EV_P_ ev_timer *w, int revents)
+ {
+ ev_check_stop (EV_A_ w);
+ }
+
+ ev_check check;
+ ev_check_init (&check, check_cb);
+ ev_check_start (EV_DEFAULT_ &check);
+ ev_loop (EV_DEFAULT_ 0);
+
+=head1 EMBEDDING
+
+Libev can (and often is) directly embedded into host
+applications. Examples of applications that embed it include the Deliantra
+Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)
+and rxvt-unicode.
+
+The goal is to enable you to just copy the neecssary files into your
+source directory without having to change even a single line in them, so
+you can easily upgrade by simply copying (or having a checked-out copy of
+libev somewhere in your source tree).
+
+=head2 FILESETS
+
+Depending on what features you need you need to include one or more sets of files
+in your app.
+
+=head3 CORE EVENT LOOP
+
+To include only the libev core (all the C<ev_*> functions), with manual
+configuration (no autoconf):
+
+ #define EV_STANDALONE 1
+ #include "ev.c"
+
+This will automatically include F<ev.h>, too, and should be done in a
+single C source file only to provide the function implementations. To use
+it, do the same for F<ev.h> in all files wishing to use this API (best
+done by writing a wrapper around F<ev.h> that you can include instead and
+where you can put other configuration options):
+
+ #define EV_STANDALONE 1
+ #include "ev.h"
+
+Both header files and implementation files can be compiled with a C++
+compiler (at least, thats a stated goal, and breakage will be treated
+as a bug).
+
+You need the following files in your source tree, or in a directory
+in your include path (e.g. in libev/ when using -Ilibev):
+
+ ev.h
+ ev.c
+ ev_vars.h
+ ev_wrap.h
+
+ ev_win32.c required on win32 platforms only
+
+ ev_select.c only when select backend is enabled (which is enabled by default)
+ ev_poll.c only when poll backend is enabled (disabled by default)
+ ev_epoll.c only when the epoll backend is enabled (disabled by default)
+ ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
+ ev_port.c only when the solaris port backend is enabled (disabled by default)
+
+F<ev.c> includes the backend files directly when enabled, so you only need
+to compile this single file.
+
+=head3 LIBEVENT COMPATIBILITY API
+
+To include the libevent compatibility API, also include:
+
+ #include "event.c"
+
+in the file including F<ev.c>, and:
+
+ #include "event.h"
+
+in the files that want to use the libevent API. This also includes F<ev.h>.
+
+You need the following additional files for this:
+
+ event.h
+ event.c
+
+=head3 AUTOCONF SUPPORT
+
+Instead of using C<EV_STANDALONE=1> and providing your config in
+whatever way you want, you can also C<m4_include([libev.m4])> in your
+F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then
+include F<config.h> and configure itself accordingly.
+
+For this of course you need the m4 file:
+
+ libev.m4
+
+=head2 PREPROCESSOR SYMBOLS/MACROS
+
+Libev can be configured via a variety of preprocessor symbols you have to define
+before including any of its files. The default is not to build for multiplicity
+and only include the select backend.
+
+=over 4
+
+=item EV_STANDALONE
+
+Must always be C<1> if you do not use autoconf configuration, which
+keeps libev from including F<config.h>, and it also defines dummy
+implementations for some libevent functions (such as logging, which is not
+supported). It will also not define any of the structs usually found in
+F<event.h> that are not directly supported by the libev core alone.
+
+=item EV_USE_MONOTONIC
+
+If defined to be C<1>, libev will try to detect the availability of the
+monotonic clock option at both compiletime and runtime. Otherwise no use
+of the monotonic clock option will be attempted. If you enable this, you
+usually have to link against librt or something similar. Enabling it when
+the functionality isn't available is safe, though, althoguh you have
+to make sure you link against any libraries where the C<clock_gettime>
+function is hiding in (often F<-lrt>).
+
+=item EV_USE_REALTIME
+
+If defined to be C<1>, libev will try to detect the availability of the
+realtime clock option at compiletime (and assume its availability at
+runtime if successful). Otherwise no use of the realtime clock option will
+be attempted. This effectively replaces C<gettimeofday> by C<clock_get
+(CLOCK_REALTIME, ...)> and will not normally affect correctness. See tzhe note about libraries
+in the description of C<EV_USE_MONOTONIC>, though.
+
+=item EV_USE_SELECT
+
+If undefined or defined to be C<1>, libev will compile in support for the
+C<select>(2) backend. No attempt at autodetection will be done: if no
+other method takes over, select will be it. Otherwise the select backend
+will not be compiled in.
+
+=item EV_SELECT_USE_FD_SET
+
+If defined to C<1>, then the select backend will use the system C<fd_set>
+structure. This is useful if libev doesn't compile due to a missing
+C<NFDBITS> or C<fd_mask> definition or it misguesses the bitset layout on
+exotic systems. This usually limits the range of file descriptors to some
+low limit such as 1024 or might have other limitations (winsocket only
+allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, might
+influence the size of the C<fd_set> used.
+
+=item EV_SELECT_IS_WINSOCKET
+
+When defined to C<1>, the select backend will assume that
+select/socket/connect etc. don't understand file descriptors but
+wants osf handles on win32 (this is the case when the select to
+be used is the winsock select). This means that it will call
+C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
+it is assumed that all these functions actually work on fds, even
+on win32. Should not be defined on non-win32 platforms.
+
+=item EV_USE_POLL
+
+If defined to be C<1>, libev will compile in support for the C<poll>(2)
+backend. Otherwise it will be enabled on non-win32 platforms. It
+takes precedence over select.
+
+=item EV_USE_EPOLL
+
+If defined to be C<1>, libev will compile in support for the Linux
+C<epoll>(7) backend. Its availability will be detected at runtime,
+otherwise another method will be used as fallback. This is the
+preferred backend for GNU/Linux systems.
+
+=item EV_USE_KQUEUE
+
+If defined to be C<1>, libev will compile in support for the BSD style
+C<kqueue>(2) backend. Its actual availability will be detected at runtime,
+otherwise another method will be used as fallback. This is the preferred
+backend for BSD and BSD-like systems, although on most BSDs kqueue only
+supports some types of fds correctly (the only platform we found that
+supports ptys for example was NetBSD), so kqueue might be compiled in, but
+not be used unless explicitly requested. The best way to use it is to find
+out whether kqueue supports your type of fd properly and use an embedded
+kqueue loop.
+
+=item EV_USE_PORT
+
+If defined to be C<1>, libev will compile in support for the Solaris
+10 port style backend. Its availability will be detected at runtime,
+otherwise another method will be used as fallback. This is the preferred
+backend for Solaris 10 systems.
+
+=item EV_USE_DEVPOLL
+
+reserved for future expansion, works like the USE symbols above.
+
+=item EV_USE_INOTIFY
+
+If defined to be C<1>, libev will compile in support for the Linux inotify
+interface to speed up C<ev_stat> watchers. Its actual availability will
+be detected at runtime.
+
+=item EV_H
+
+The name of the F<ev.h> header file used to include it. The default if
+undefined is C<< <ev.h> >> in F<event.h> and C<"ev.h"> in F<ev.c>. This
+can be used to virtually rename the F<ev.h> header file in case of conflicts.
+
+=item EV_CONFIG_H
+
+If C<EV_STANDALONE> isn't C<1>, this variable can be used to override
+F<ev.c>'s idea of where to find the F<config.h> file, similarly to
+C<EV_H>, above.
+
+=item EV_EVENT_H
+
+Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea
+of how the F<event.h> header can be found.
+
+=item EV_PROTOTYPES
+
+If defined to be C<0>, then F<ev.h> will not define any function
+prototypes, but still define all the structs and other symbols. This is
+occasionally useful if you want to provide your own wrapper functions
+around libev functions.
+
+=item EV_MULTIPLICITY
+
+If undefined or defined to C<1>, then all event-loop-specific functions
+will have the C<struct ev_loop *> as first argument, and you can create
+additional independent event loops. Otherwise there will be no support
+for multiple event loops and there is no first event loop pointer
+argument. Instead, all functions act on the single default loop.
+
+=item EV_MINPRI
+
+=item EV_MAXPRI
+
+The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to
+C<EV_MAXPRI>, but otherwise there are no non-obvious limitations. You can
+provide for more priorities by overriding those symbols (usually defined
+to be C<-2> and C<2>, respectively).
+
+When doing priority-based operations, libev usually has to linearly search
+all the priorities, so having many of them (hundreds) uses a lot of space
+and time, so using the defaults of five priorities (-2 .. +2) is usually
+fine.
+
+If your embedding app does not need any priorities, defining these both to
+C<0> will save some memory and cpu.
+
+=item EV_PERIODIC_ENABLE
+
+If undefined or defined to be C<1>, then periodic timers are supported. If
+defined to be C<0>, then they are not. Disabling them saves a few kB of
+code.
+
+=item EV_IDLE_ENABLE
+
+If undefined or defined to be C<1>, then idle watchers are supported. If
+defined to be C<0>, then they are not. Disabling them saves a few kB of
+code.
+
+=item EV_EMBED_ENABLE
+
+If undefined or defined to be C<1>, then embed watchers are supported. If
+defined to be C<0>, then they are not.
+
+=item EV_STAT_ENABLE
+
+If undefined or defined to be C<1>, then stat watchers are supported. If
+defined to be C<0>, then they are not.
+
+=item EV_FORK_ENABLE
+
+If undefined or defined to be C<1>, then fork watchers are supported. If
+defined to be C<0>, then they are not.
+
+=item EV_MINIMAL
+
+If you need to shave off some kilobytes of code at the expense of some
+speed, define this symbol to C<1>. Currently only used for gcc to override
+some inlining decisions, saves roughly 30% codesize of amd64.
+
+=item EV_PID_HASHSIZE
+
+C<ev_child> watchers use a small hash table to distribute workload by
+pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more
+than enough. If you need to manage thousands of children you might want to
+increase this value (I<must> be a power of two).
+
+=item EV_INOTIFY_HASHSIZE
+
+C<ev_staz> watchers use a small hash table to distribute workload by
+inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),
+usually more than enough. If you need to manage thousands of C<ev_stat>
+watchers you might want to increase this value (I<must> be a power of
+two).
+
+=item EV_COMMON
+
+By default, all watchers have a C<void *data> member. By redefining
+this macro to a something else you can include more and other types of
+members. You have to define it each time you include one of the files,
+though, and it must be identical each time.
+
+For example, the perl EV module uses something like this:
+
+ #define EV_COMMON \
+ SV *self; /* contains this struct */ \
+ SV *cb_sv, *fh /* note no trailing ";" */
+
+=item EV_CB_DECLARE (type)
+
+=item EV_CB_INVOKE (watcher, revents)
+
+=item ev_set_cb (ev, cb)
+
+Can be used to change the callback member declaration in each watcher,
+and the way callbacks are invoked and set. Must expand to a struct member
+definition and a statement, respectively. See the F<ev.v> header file for
+their default definitions. One possible use for overriding these is to
+avoid the C<struct ev_loop *> as first argument in all cases, or to use
+method calls instead of plain function calls in C++.
+
+=head2 EXAMPLES
+
+For a real-world example of a program the includes libev
+verbatim, you can have a look at the EV perl module
+(L<http://software.schmorp.de/pkg/EV.html>). It has the libev files in
+the F<libev/> subdirectory and includes them in the F<EV/EVAPI.h> (public
+interface) and F<EV.xs> (implementation) files. Only the F<EV.xs> file
+will be compiled. It is pretty complex because it provides its own header
+file.
+
+The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
+that everybody includes and which overrides some configure choices:
+
+ #define EV_MINIMAL 1
+ #define EV_USE_POLL 0
+ #define EV_MULTIPLICITY 0
+ #define EV_PERIODIC_ENABLE 0
+ #define EV_STAT_ENABLE 0
+ #define EV_FORK_ENABLE 0
+ #define EV_CONFIG_H <config.h>
+ #define EV_MINPRI 0
+ #define EV_MAXPRI 0
+
+ #include "ev++.h"
+
+And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
+
+ #include "ev_cpp.h"
+ #include "ev.c"
+
+
+=head1 COMPLEXITIES
+
+In this section the complexities of (many of) the algorithms used inside
+libev will be explained. For complexity discussions about backends see the
+documentation for C<ev_default_init>.
+
+All of the following are about amortised time: If an array needs to be
+extended, libev needs to realloc and move the whole array, but this
+happens asymptotically never with higher number of elements, so O(1) might
+mean it might do a lengthy realloc operation in rare cases, but on average
+it is much faster and asymptotically approaches constant time.
+
+=over 4
+
+=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
+
+This means that, when you have a watcher that triggers in one hour and
+there are 100 watchers that would trigger before that then inserting will
+have to skip those 100 watchers.
+
+=item Changing timer/periodic watchers (by autorepeat, again): O(log skipped_other_timers)
+
+That means that for changing a timer costs less than removing/adding them
+as only the relative motion in the event queue has to be paid for.
+
+=item Starting io/check/prepare/idle/signal/child watchers: O(1)
+
+These just add the watcher into an array or at the head of a list.
+=item Stopping check/prepare/idle watchers: O(1)
+
+=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
+
+These watchers are stored in lists then need to be walked to find the
+correct watcher to remove. The lists are usually short (you don't usually
+have many watchers waiting for the same fd or signal).
+
+=item Finding the next timer per loop iteration: O(1)
+
+=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
+
+A change means an I/O watcher gets started or stopped, which requires
+libev to recalculate its status (and possibly tell the kernel).
+
+=item Activating one watcher: O(1)
+
+=item Priority handling: O(number_of_priorities)
+
+Priorities are implemented by allocating some space for each
+priority. When doing priority-based operations, libev usually has to
+linearly search all the priorities.
+
+=back
+
+
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